Modern wind turbines adjust rotor blade pitch for several reasons. One reason is to improve blade efficiency by adapting the blade aerodynamics to optimize efficiency with wind speed changes. Another reason is to take the blades to an unloaded, or feathered condition, in the event that wind speed exceeds the maximum safe rated speed or in the event of fault conditions.
Modern wind turbines may have two separate and independent blade pitch control systems: (1) a main blade pitch control system that is used to optimize performance during normal operating conditions, and (2) a safety pitch control system that is adapted to override the main blade pitch control system and to cause each of the blades to move toward an unloaded or feathered condition in the event of a sensed fault or in the event that the wind speed exceeds a predetermined maximum.
The main blade pitch control system is typically controlled by a closed-loop pitch-axis controller. This controller automatically adjusts the operational state of the turbine in order to keep it on some pre-defined operating curve or characteristic. The controller changes the blade pitch, or angle, through a blade pitch actuator. This actuator may be either electrically or hydraulically powered.
The safety pitch control system may be separate and distinct from the main blade pitch control system. Its function is to bring the turbine to a safe condition in the event of a problem. The safety system normally does not depend on adaptive electronics. Rather, the actuator is normally hard-wired to a battery through normally-open relay contacts that selectively close under a fault condition or in the event of an overspeed condition.
Heretofore, the pitch-axis controller, the battery and the electro-mechanical actuator for varying the pitch of each blade, were located in the hub. These were components of a safety pitch control system. This increased the mass of the rotating hub, required the use of premium components, and presented space constraints within the hub.
Thus, there would be a distinct advantage to moving or relocating the batteries and the control electronics to the nacelle.